1. Field of the Invention
The present invention relates to a fuel pump, which draws fuel and discharges the drawn fuel after pressurizing the drawn fuel.
2. Description of Related Art
For example, Japanese Unexamined Patent Publication No. 2005-127290A teaches a fuel pump that includes a rotatable member and a flow passage member. The rotatable member is configured into a generally circular disk form and includes a plurality of blades and a ring portion. The blades are arranged one after another in a circumferential direction. The ring portion is annular and is placed radially outward of the blades. The flow passage member includes a receiving portion (receiving chamber) and a flow passage groove. The receiving portion rotatably receives the rotatable member. The flow passage groove forms a pump flow passage that conducts the fuel in a rotational direction of the rotatable member and pressurizes the fuel in cooperation with the rotatable member upon rotation of the rotatable member. The flow passage groove is configured into an arcuate form arcuately extending in the circumferential direction.
In the above fuel pump, which has the rotatable member including the ring portion, which is annular and is placed radially outward of the blades, the rotatable member can be rotated while the axial end surface of the ring portion slides along the inner wall surface of the receiving portion. Therefore, in the pressurizing process of the fuel, it is possible to limit or minimize a leakage of the fuel from the pump flow passage to a radially outer side of the rotatable member where the fuel pressure is lower than that of the pump flow passage.
That is, a pump efficiency can be improved. Here, the pump efficiency is expressed by (P×Q)/(T×N). In this equation, “T” denotes a torque of a motor device, which drives the rotatable member, and “N” denotes a rotational speed of the motor device. Furthermore, “P” denotes a fuel pressure of the discharged fuel, and “Q” denotes the amount of the discharged fuel.
However, since the axial slide gap, which is formed between the axial end surface of the ring portion and the slide surface provided in the inner wall surface of the receiving portion, is made very small, contaminants, which are contained in the fuel and are drawn into this axial slide gap, may possibly cause an increase in wearing of the rotatable member and the flow passage member and/or an increase in the slide resistance between the rotatable member and the flow passage member to result in a deterioration of the pump efficiency.
In the case of the fuel pump recited in Japanese Unexamined Patent Publication No. 2005-127290A, a discharge port is formed to axially oppose the axial end surface of the ring portion, so that the portion of the pump flow passage, which is located adjacent to the discharge port, radially extends across the axial end surface of the ring portion.
In the case of the pump flow passage constructed in the above-described manner, the contaminants, which are drawn into the axial slide gap, are dragged by the rotatable member upon the rotation of the rotatable member and are discharged from the discharge port, which radially extends across the axial end surface of the ring portion. With this construction, it is possible to alleviate the disadvantages associated with the intrusion of the contaminants in the axial slide gap.
However, as discussed above, the portion of the pump flow passage radially extends across the axial end surface of the ring portion, so that the pressurized fuel flows into not only the discharge port but also into the radial gap between the outer peripheral wall surface of the ring portion and the inner peripheral wall surface of the receiving portion. This radial gap is also communicated with the pump flow passage, so that the pump efficiency may possibly be deteriorated.